Method for removing an electronic component from a substrate

ABSTRACT

A system and method for removing an electronic component from a substrate is described. In one embodiment, a method in accordance with the invention includes initially preheating a substrate, wherein an electronic component (such as a microchip or discrete electronic component) is attached to the substrate by one or more solder connections. A thermally conductive picker head is applied to the electronic component to quench the electronic component and generate a temperature gradient across the solder connections. Tension is applied to the electronic component using the picker head. The substrate is then heated until a melting point is reached at the interface between the substrate and the solder connections. When the melting point is reached, the tension applied by the picker head removes the electronic component from the substrate. Most if not all of the solder associated with the solder connections is removed with the electronic component.

BACKGROUND

1. Field of the Invention

This invention relates to systems and methods for removing electroniccomponents, such as microchips, from substrates.

2. Background of the Invention

High-end microelectronic modules often include one or more microchipsmounted to a carrier to provide a desired level of performance andfunctionality. Often, one or more microchips on a carrier substrate needto be replaced to repair and/or improve the performance of amicroelectronic module. When removing a microchip, the solder on thecarrier pads underneath the microchip also typically needs to be removedso that another microchip can be attached.

Several techniques currently exist for removing solder from carrier padsor other parts of a substrate. One technique involves utilizing a porousmetal block to remove solder from a substrate. Such a porous metal blockmay include protrusions that are placed in contact with molten solder onthe substrate to absorb the solder through capillary action. The porousmetal block may be designed with an interconnected and uniform porositythat provides uniform absorption across the block surface. The numberand dimensions of the protrusions on the block may vary based on theapplication. Although effective, this technique can be costly andtime-consuming.

Another technique is to use an acid such as nitric acid to dissolve thesolder on the carrier. For example, the solder may be removed by dippingthe substrate in fuming nitric acid. Unfortunately, such a technique cancontaminate the substrate surface and may be difficult to implement forchip removal. Furthermore, acids such as nitric acid can be hazardousand difficult to handle. Nitric acid in particular is corrosive,reactive, and dangerous to touch or inhale.

In view of the foregoing, what are needed are systems and methods toremove electronic components, such as microchips, from carriersubstrates. Ideally, such systems and methods would be effective toremove most if not all of the solder that connects the electroniccomponents to the substrates. Such systems and methods would alsoideally not require chemicals such as fluxes or cleaning agents toremove the solder.

SUMMARY

The invention has been developed in response to the present state of theart and, in particular, in response to the problems and needs in the artthat have not yet been fully solved by currently available systems andmethods. Accordingly, the invention has been developed to providesystems and methods to remove electronic components, such as microchips,from carrier substrates. The features and advantages of the inventionwill become more fully apparent from the following description andappended claims, or may be learned by practice of the invention as setforth hereinafter.

Consistent with the foregoing, a method for removing an electroniccomponent from a substrate is disclosed herein. In one embodiment, sucha method includes initially preheating a substrate, wherein anelectronic component (such as a microchip or discrete electroniccomponent) is attached to the substrate by one or more solderconnections. A thermally conductive picker head is applied to theelectronic component to quench the electronic component and generate atemperature gradient across the solder connections. Tension is appliedto the electronic component using the picker head. The substrate is thenheated until a melting point is reached at the interface between thesubstrate and the solder connections. When the melting point is reached,the tension applied by the picker head removes the electronic componentfrom the substrate. Most if not all of the solder associated with thesolder connections is removed with the electronic component.

In another aspect of the invention, a system for removing an electroniccomponent from a substrate is disclosed herein. In one embodiment, sucha system includes a heating device to heat a substrate, wherein anelectronic component such as a microchip is attached to the substrate byone or more solder connections. A thermally conductive picker head isplaced in physical contact with the electronic component to quench theelectronic component and generate a temperature gradient across the oneor more solder connections. The thermally conductive picker headincludes a flat contact surface that is distributed substantially evenlyacross the electronic component. This enables heat to be conducted fromthe electronic component evenly, thereby generating a uniformtemperature gradient across the solder connections. This will allow theelectronic component along with most or all of the solder to be removedfrom the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through use of theaccompanying drawings, in which:

FIG. 1 is a high-level block diagram showing one example of a system forremoving an electronic component from a substrate;

FIG. 2 shows a first stage of a component removal process wherein asubstrate of an electronic module is preheated;

FIG. 3 shows a second stage of a component removal process wherein apicker head attaches to and quenches an electronic component;

FIG. 4 shows a third stage of a component removal process wherein aninterface between solder connections and a substrate is heated to amelting point and an electronic component is removed from the substratealong with most if not all of the solder associated with the solderconnections;

FIG. 5 shows an alternative third stage of a component removal processwhere the interface between the solder connections and the electroniccomponent is heated to the melting point and the electronic component isremoved from the substrate to leave most if not all of the solder on thesubstrate;

FIG. 6A shows one example of a picker head used to effectively quench anelectronic component and create a desired temperature gradient acrossthe solder connections;

FIGS. 6B through 6E show various patterns of apertures on a contactsurface of the picker head to enable the picker head to more evenlyconvey heat away from the electronic component;

FIG. 7 is a flow chart showing one embodiment of a method for removingan electronic component from a substrate; and

FIG. 8 is a flow chart showing an alternative embodiment of a method forremoving an electronic component from a substrate.

DETAILED DESCRIPTION

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the Figures herein,could be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of the invention, as represented in the Figures, is notintended to limit the scope of the invention, as claimed, but is merelyrepresentative of certain examples of presently contemplated embodimentsin accordance with the invention. The presently described embodimentswill be best understood by reference to the drawings, wherein like partsare designated by like numerals throughout.

Referring to FIG. 1, one example of a system 100 for removing anelectronic component 102 from a substrate 104 is illustrated. For thepurposes of this disclosure, an “electronic component” may include amicrochip, a semiconductor die, a discrete electronic component, orother electronic circuit or device. Similarly, a “substrate” may includea printed circuit board (PCB), ceramic-based substrate, or other carriersubstrate used to mechanically support and electrically connectelectronic components. The electronic component 102 and substrate 104together form part of a “microelectronic module” 110, which may alsoinclude other electronic components such as other chips or discretecomponents.

As shown, the system 100 includes a heating device 106 to heat thesubstrate 104 to a desired temperature. The heating device 106 may heatthe substrate 104 by one or more of conduction (e.g., a heat plate),radiation (e.g., an infrared heater), or convection (e.g., hot air)through the underside of the substrate 104. A thermally conductivepicker head 108 is provided to physically attach to and quench (i.e.,cool) the electronic component 102. Ideally, the picker head 108 usesvacuum to attach to the electronic component 102. Alternatively, thepicker head 108 could include mechanical means to physically grip theelectronic component. Whatever the physical attachment means used, thepicker head 108 is designed to create an intimate bond with theelectronic component 102 to provide a good thermal interface. As will beexplained in more detail hereafter, quenching the electronic component102 will produce a desired temperature gradient across solderconnections (e.g., lead or lead-free solder connections) electricallyconnecting the electronic component 102 to the substrate 104. When theelectronic component 102 is removed, the temperature gradient willideally enable the solder connections to be removed from the substrate104 with the electronic component 102, thereby providing a cleansubstrate 104 that will allow a new electronic component 102 to beattached.

One or more control modules 112 a-c may be provided to control theheating device 106 and the picker head 108. A temperature control module112 a may be used to control the temperature of the heating device 106.The temperature control module 112 a may also optionally control aheating or cooling device in the picker head 108. A position/tensioncontrol module 112 b may control the position of the picker head 108and/or the tension placed on the electronic component 102 by the pickerhead 108. For example, the position/tension control module 112 b mayraise or lower the picker head 108 with respect to the electroniccomponent 102 or place a desired amount of tension on the electroniccomponent 102 after the picker head 108 has attached to the electroniccomponent 102. A vacuum control module 112 c may control the vacuumneeded to physically attach to the electronic component 102. Each of thecontrol modules 112 a-c may operate in an automated fashion (such asusing computers, electronic controllers, or the like) or provide manualcontrols for operation by users. The control modules 112 a-c may beembodied as different modules or may be integrated into a single module.

In selected embodiments, the system 100 is operated in an inertatmosphere to minimize oxidation. For example, the system 100 may beoperated in a chamber filled with an inert gas (e.g., N₂) or mixture ofgases. This will reduce or minimize the oxidation of solder connections,carrier pads, or other materials during the component removal process.

Referring to FIG. 2, a diagram showing a first stage of a componentremoval process is illustrated. In this stage, the picker head 108 isseparated from the electronic component 102 and the substrate 104 ispreheated to a temperature below the melting point of the solderconnections 200. While the substrate 104 is preheated, the picker head108 is maintained at a temperature significantly below the temperatureof the substrate 104. This can be accomplished, for example, by keepingthe picker head 108 a significant distance away from the heating device106 or by cooling or maintaining the picker head 108 at a desiredtemperature with a cooling device, heat dissipation device, or the like.The solder connections 200 between the electronic component 102 and thesubstrate 104 may include solder balls, C4 connections, solder columnconnections, or the like. The solder connections 200 may connectmetalized pads 202 on the electronic component 102 to metalized pads 204on the substrate 104.

Referring to FIG. 3, a diagram showing a second stage of a componentremoval process is illustrated. In this stage, once the substrate 104 ispreheated to a desired temperature below the melting point of the solderconnections 200, the picker head 108 is brought into contact with theelectronic component 102. This quenches the electronic component 102 togenerate a large temperature gradient across the electronic module 110,and more particularly across the solder connections 200. As will beexplained in more detail hereafter, the picker head 108 may be designedin such a way that heat is quickly and evenly conveyed away from theelectronic component 102, thereby producing a substantially evenin-plane temperature across the electronic component 102. This will helpto ensure that the solder connections 200 reach the melting point atsubstantially the same time. For a similar reason, the heating device106 should be designed to provide substantially even heating of thesubstrate 104.

Once the picker head 108 is brought into contact with the electroniccomponent 102, the vacuum is activated to enable the picker head 108 toattach to the component 102. This will allow tension to be applied tothe electronic component 102 in a direction substantially perpendicularto the substrate 104. This will also create more intimate contactbetween the picker head 108 and the electronic component 102 to improvethe thermal interface. If desired, a thermally conductive material (suchas a compliant thermal interface) may be placed between the picker head108 and the electronic component 102 to improve the thermal interface.Ideally, the mating surfaces of the picker head 108 and the electroniccomponent 102 are as flat as possible to prevent or reduce vacuum leaksand provide a good physical bond. Vacuum leaks are undesirable not onlybecause of the reduction in attachment strength, but also because leaksmay create hot or cold spots on the electronic component 102, which mayin turn cause different solder connections 200 to reach the meltingpoint at different times.

Referring to FIG. 4, a diagram showing a third stage of a componentremoval process is illustrated. In this stage, once the picker head 108has quenched the electronic component 102 and placed the electroniccomponent 102 under a state of tension, the temperature of the substrate104 is ramped up until the solder connections 200 reach the meltingpoint at the interface 400 between the substrate 104 (and morespecifically the carrier pads 204 on the substrate 104) and the solderconnections 200. The ramp rate may be optimized to achieve the highesttemperature gradient (achieved with a higher ramp rate) whilemaintaining in-plane temperature uniformity (achieved with a lower ramprate). In selected embodiments, the ramp rate is between 0.1 and 2degrees C. per second. The in-plane temperature uniformity may alsodepend on factors such as the gas flow rate through the chamber, thecharacteristics of the heating device 106, the substrate 104 thermalproperties, the picker head 108 thermal properties, and the like.

Once the melting point is reached, the tension on the electroniccomponent 102 causes the electronic component 102 to separate from thesubstrate 104. As shown, because melting occurs first at or near theinterface 400 been the carrier pads 204 and the solder connections 200,most if not all of the solder is removed with the electronic component102, leaving a minimal amount of solder on the carrier pads 204. Thiswill ideally allow another electronic component 102 to be attached tothe substrate 104 with minimal cleaning of the carrier pads 204. Thisresult is attributable at least in part to the large temperaturegradient generated across the solder connections 200.

Referring to FIG. 5, a diagram showing an alternative embodiment of athird stage of a component removal process is illustrated. In thisembodiment, the temperatures of the picker head 108 and the substrate104 are reversed to generate a temperature gradient in the oppositedirection. This will cause the solder connections 200 to first reach themelting point at the interface 500 between the solder connections 200and the metalized pads 202 of the electronic component 102. Once themelting point is reached, the electronic component 102 separates fromthe substrate 104, leaving most if not all of the solder on thesubstrate 104. Such an embodiment may be useful where the electroniccomponent 102 is to be reused or the substrate 104 is to be discarded.Because of the large temperature gradient across the solder connections200, most if not all of the solder is removed from the electroniccomponent 102.

Referring to FIG. 6A, as previously mentioned, the picker head 108 maybe designed in such a way that heat is quickly and evenly conveyed awayfrom the electronic component 102. This will ideally produce asubstantially even in-plane temperature across the electronic component102. At the same time, the picker head 108 is designed to attach to andapply a pull force on the electronic component 102 using the vacuumpreviously described. In certain embodiments, the picker head 108 isdesigned to exert a constant pull force in the range of 0.1 to 5 kgf.

In selected embodiments, the picker head 108 is designed with asubstantially flat contact surface 600 which is distributedsubstantially evenly across the electronic component 102. This willideally achieve a substantially uniform in-plane temperature. In certainembodiments, this may be accomplished by providing a number of apertures602 evenly distributed across the contact surface 600 to apply vacuum tothe electronic component 102. This design will eliminate large gaps orholes in the thermal interface that may create hot or cold spots on theelectronic component 102. FIGS. 6B through 6E show various examples of acontact surface 600 with apertures 602 that is designed to apply avacuum to an electronic component 102 while still creating a goodthermal interface. As can be observed from each of the embodiments,contact areas are provided across the contact surfaces 600, withoutlarge gaps or holes, to provide effective heat dissipation.

Other characteristics of the picker head 108, such as the mass of thepicker head 108, the material of the picker head 108, and thetemperature control of the picker head 108 may also affect the speed atwhich heat is conveyed away from the electronic component 102. Inselected embodiments, the picker head 108 is fabricated from a highlythermally conductive metal, such as aluminum or copper, to convey heataway from the electronic component 102. In other embodiments, materialssuch as diamond, polycrystalline diamond (PCD), or the like may be usedto convey heat away from the electronic component 102. As previouslymentioned, materials such as thermal greases or pastes may be used atthe interface between the picker head 108 and the electronic component102 to improve the thermal conductivity.

Referring to FIG. 7, one embodiment of a method 700 for removing anelectronic component 102 from a substrate 104 is illustrated. Such amethod 700 may be used with the hardware illustrated in FIGS. 1 through6 or with other hardware. As shown, the method 700 initially positions702 an electronic module 110 in a chamber. Positioning 702 theelectronic module 110 may include placing the electronic module 110 on aheating device 106 and aligning the electronic module 110 beneath apicker head 108 using guide pins or other alignment means. Once theelectronic module 110 is positioned 702 in the chamber, the chamber ispurged 704 of oxidizing gases. In certain embodiments, a purge time maybe allowed to pass to allow the chamber to reach low enough oxygencontent. Purging 704 may also include replacing the oxidizing gases withan inert gas or mixture of gases such as nitrogen gas.

Once the chamber is purged 704 of oxidizing gases, the method 700preheats 706 the electronic module 110 to a temperature below themelting point of the solder connections 200, such as 1 to 30 degrees C.below the melting point. At this point the picker head 108 is separatedfrom the electronic component 102 and cooled or maintained at atemperature below that of the electronic module 110, such as at or nearambient temperature. The picker head 108 is then applied 708 to theelectronic component 102 to quench the electronic component 102 andgenerate a temperature gradient across the electronic module 110. Inselected embodiments, using the techniques described herein, atemperature gradient of greater than 100° C. may be generated across theelectronic module 110. Applying 708 the picker head 108 may also includeactivating the vacuum to cause the picker head 108 to attach to andquench the electronic component 102. Once the picker head 108 hasattached to the electronic component 102, tension is applied 710 to theelectronic component 102. In certain embodiments, the tension is enoughto generate about 0.02 to 0.5 MPa of stress on the solder connections200. In certain embodiments, the tension is applied to the electroniccomponent 102 in a direction substantially perpendicular to thesubstrate 104.

The substrate 104 is then heated 712 until the solder connections 200reach the melting point at or near the interface 400 between the solderconnections 200 and the carrier pads 204 of the substrate 104. When themelting point is reached, the tension applied by the picker head 108will remove 714 the electronic component 102 from the substrate 104along with most if not all of the solder. Upon removal, the electronicmodule 110 may be maintained at a temperature above the solder meltingpoint to allow any residual solder on the substrate 104 to reflow. Theelectronic module 110 may then be cooled down in a controlledenvironment (e.g., an inert atmosphere) until the temperature of theelectronic module 110 is low enough to avoid oxidation.

Referring to FIG. 8, an alternative embodiment of a method 800 forremoving an electronic component 102 from a substrate 104 isillustrated. As shown, the method 800 is substantially identical to themethod 700 illustrated in FIG. 7, except that the method steps 706, 708have been changed. In this embodiment, instead of keeping the pickerhead 108 separated from the electronic module 110 during a preheat step802, the picker head 108 is placed in contact with the electronic module110. Upon completing the preheat step 802, the picker head 108 is cooledto a desired temperature using a cooling device, heat dissipationdevice, or the like. This will quench the electronic component 102 togenerate a desired temperature gradient across the electronic module110. Once a desired temperature gradient is achieved, the substrate 104is ramped 712 to a final temperature and the electronic component 102 isremoved 714 in the manner previously described.

The systems and methods disclosed herein may be embodied in otherspecific forms without departing from their spirit or essentialcharacteristics. The described embodiments are to be considered in allrespects only as illustrative and not restrictive. The scope of theinvention is, therefore, indicated by the appended claims rather than bythe foregoing description. All changes which come within the meaning andrange of equivalency of the claims are to be embraced within theirscope.

The invention claimed is:
 1. A method for removing an electroniccomponent from a substrate, wherein the electronic component is attachedto the substrate by at least one solder connection, the methodcomprising: preheating the substrate; applying a thermally conductivepicker head to the electronic component to quench the electroniccomponent and generate a temperature gradient across the electroniccomponent and substrate; applying, using the thermally conductive pickerhead, tension to the electronic component while drawing heat away fromthe electronic component through a thermally conductive interfacebetween the electronic component and the thermally conductive pickerhead; heating the substrate until a melting point is reached at aninterface between the substrate and the at least solder connection; andremoving the electronic component from the substrate.
 2. The method ofclaim 1, wherein heating the substrate comprises at least one of heatingthe substrate by conduction, heating the substrate by radiation, andheating the substrate by convection.
 3. The method of claim 1, whereinthe temperature gradient is greater than 100° C.
 4. The method of claim1, further comprising cooling the thermally conductive picker head toincrease the temperature gradient.
 5. The method of claim 4, whereincooling comprises pre-cooling the thermally conductive picker head priorto applying the thermally conductive picker head to the electroniccomponent.
 6. The method of claim 4, wherein cooling comprises coolingthe thermally conductive picker head after applying the thermallyconductive picker head to the electronic component.
 7. The method ofclaim 1, further comprising regulating a temperature of the thermallyconductive picker head to control the temperature gradient.
 8. Themethod of claim 1, wherein applying the thermally conductive picker headto the electronic component comprises applying a vacuum to theelectronic component.
 9. The method of claim 8, wherein applying thethermally conductive picker head to the electronic component comprisesapplying a substantially flat contact surface to the electroniccomponent.
 10. The method of claim 9, wherein applying the substantiallyflat contact surface to the electronic component comprises substantiallyevenly distributing the substantially flat contact surface across theelectronic component.
 11. The method of claim 1, wherein applyingtension to the electronic component comprises applying tension in adirection substantially perpendicular to the substrate.